A simplified pictorial version of a unit fuel cell is shown in FIG. 1. The fuel cell 100 is essentially composed of two chambers: the anode compartment 102 (including the anode 110) where fuel is oxidized and the cathode compartment 104 (including the cathode 112) where the reduction occurs. The energy generated from the reaction can be utilized if the flow of electrons occurs through the external circuit 106. Passage of electrons from anode 110 to cathode 112 through the membrane 108, made of a material such as polyelectrolyte, reduces the efficiency of the reaction and the performance of the fuel cell 100 is diminished. However, while the membrane 108 must minimize transport of electrons, migration of protons across the membrane 108 from anode 110 to cathode 112 is used to maintain a balanced electric charge across the membrane 108 and in the two cells. It is desirable to have a high proton conductivity and high electrical resistance in the membrane 108, which are relatively uncommon properties of materials. However, these properties are possessed by the Nafion-based family of polysulfonated fluoropolymers.
Nafion polymers can be cast from solution as thin films and/or pressed and extruded into form from powder to make thin polyelectrolyte membranes (PEMs) for fuel cells. However, these thin membranes are delicate and a high water content must be maintained to function properly, thereby limiting the operational temperature of the fuel cell to less than 100° C. This low maximum operating temperature limits the selection of catalysts available for promoting the redox reactions to the most active in this temperature range, which are typically the platinum-based catalysts. The low operating temperature also requires that fuels must be very low in carbon monoxide (CO), because at these low temperatures CO binds tenaciously to platinum and inhibits the oxidation reaction at the anode. Therefore, the fuel typically is purified hydrogen rather than hydrogen derived from reforming alcohols or alkanes to keep the CO content low. Note that platinum-ruthenium catalysts are less prone to CO poisoning than pure platinum catalysts. Similar benefits may exist with other catalyst systems.
FIG. 2 shows a practical rendition of a fuel cell 200 with the appropriate placement of the electrode structures pressed into contact with the PEM 202 and the orthogonal flow channels carrying fuel to the anode 204 and oxygen to the cathode 206. The byproduct of the cathodic reaction is water and this is removed along the oxygen flow path 208. Generally, an assembly of single unit fuel cells is included in a fuel cell stack. Considerable supporting structure is required to configure the membranes and hold them in place. The weight of these supporting structures is generally about 75% of the total weight of a standard fuel cell.
Accordingly, a better membrane arrangement which addresses the problems associated with typical fuel cell stacks would be beneficial to advancing the abilities of fuel cells and the use of fuel cells in energy generation.